This invention relates to a pyrometallurgical process for producing brass from materials such as dusts from brass factory furnace emissions which contain significant quantities of oxidized zinc. Another common material containing oxidized zinc which may be used to produce brass in accordance with the invention is metallic fines from reclamation plants.
Brass producing plants annually generate millions of pounds of furnace emission dust, ball mill fines, and other byproducts containing zinc and copper values. The environmental restrictions recently imposed on brass mills increases the availability of these materials, and therefore, it is expected that increased quantities will be available in the future. Accordingly, there is a growing necessity for a process by which such byproducts can be economically treated to recover metallic values at the brass factory.
Typically, furnace emission dusts comprise a mixture of oxides of copper and zinc, containing trace amounts of lead and iron, with the zinc oxide making up about 70% to 90% of the total dust weight. The weight ratio of copper and zinc oxides in ball mill fines from reclamation plants is dependant on the source of this material.
In U.S. Pat. Ser. No. 3,909,243 to McKewan, a process is disclosed for recovering both brass and zinc from metallurgical residues by a carbon floatation method. Brass, zinc, and zinc oxide containing materials are charged into a furnace which is heated up to about 1250.degree. C. After the brass has melted and sunk to the bottom, carbon is added to reduce the zinc oxide to zinc metal, which is produced in vapor form. The zinc vapor is then removed and condensed, and molten slag and brass are periodically drawn off the furnace. While this technique shows promise for recovering metal values from brass factory waste materials, it requires the collection and condensation of zinc vapor. Because the equipment to handle zinc vapor is elaborate and expensive, this aspect of the McKewan process represents a significant disadvantage if a recovery procedure inexpensive enough to be set up at the site of the brass mill is desired.